In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water and an organic material such as a monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof an ink-receiving or image-receiving layer, and includes those intended for reflection viewing, which have an opaque support, and those intended for viewing by transmitted light, which have a transparent support.
A desirable characteristic of inkjet recording elements is the capability to dry quickly after printing. To this end, porous recording elements have been developed which provide nearly instantaneous drying as long as they have sufficient thickness and pore volume to effectively contain the liquid ink. For example, a porous recording element can be manufactured by cast coating, in which a particulate-containing coating is applied to a support and is dried in contact with a polished smooth surface.
Inkjet prints, prepared by printing onto inkjet recording elements, are potentially subject to environmental degradation. They are especially vulnerable to damage resulting from contact with water and atmospheric gases such as ozone. The damage resulting from post-imaging contact with water can take the form of water spots resulting from deglossing of the top coat, dye smearing due to unwanted dye diffusion, and even gross dissolution of the image recording layer. Ozone bleaches inkjet dyes resulting in loss of density.
To overcome these deficiencies inkjet prints are often laminated. However, lamination is expensive since it requires a separate roll of material. Print protection can also be provided by coating a polymer solution or dispersion onto the surface of an inkjet element after the image is formed. The aqueous coating solutions are often polymer dispersions capable of film formation when water is removed. However, due to the wide variety of surface properties, it is difficult to formulate an aqueous polymer solution to be universally compatible to all inkjet receivers.
Numerous publications teach the concept of fusible organic particles as an overcoat layer of a inkjet recoding media in order to achieve fast ink absorption before fusing and image protection after fusing.
For example, EP 0858905 discloses the preparation of a recording medium comprising a porous outermost layer by coating and drying a particulate thermoplastic resin above its glass transition temperature (Tg), but below its minimum film formation temperature (MFFT). Heat treatment of the recording medium after printing renders the outermost layer non-porous or fusion-bonded. EP 0858906 discloses a recording media comprising a base material and a porous surface layer containing particles of a thermoplastic resin, wherein the breadth of the particle size distribution of the particles of the thermoplastic resin is within 3σ, and the proportion of particles having a particle size at most a fifth of the average particle size of the particles of the thermoplastic resin is 10% or lower.
The commonly assigned, co-pending U.S. Ser. No. 10/289,607, filed Nov. 7, 2002 by Yau et al., titled “Inkjet Printing Method” and U.S. Ser. No. 10/289,862, filed Nov. 7, 2002 by Yau et al., titled “Inkjet Recording Element,” both hereby incorporated by reference in their entirety, teach the use of high Tg monodisperse particles in combination with a low Tg hydrophobic binder in an ink-receiving layer to provide an inkjet media exhibiting rapid ink absorption. Fusing of such printed media converts the ink-receiving layer to a transparent water-resistant and stain-resistant layer. However, certain problems have been associated with an inkjet recording element in which a single layer of a fusible polymer-particle layer is placed on a substrate. First, poor adhesion of the fused layer to the support may occur and, second, the fused layer may turn hazy or lose gloss appearance with time due to the interaction or incompatibility with components from the applied ink, for example, humectants.
Inkjet recording elements having a multi-layer coating construction above a support are known. For example, EP 0858905, EP 0858906, EP 1160097 A3 (=U.S. 2002008747), EP1188574, JP59222381, U.S. Pat. Nos. 6,114,020, and 6,357,871 all teach a porous ink-transporting topcoat of thermally fusible particles residing on a porous ink-retaining layer. Upon printing, the colorant in the inkjet ink is intended to pass through the topcoat and into an ink-retaining layer. The topcoat layer is then sealed to afford a water and stain resistant print. Such topcoats containing thermally fusible particles typically either contain a binder or are thermally sintered to provide a level of mechanical integrity to the layer prior to the imaging and fusing steps. The porous ink-retaining underlying layer is light diffusive and, therefore, is not suitable for transparency media. In addition, the optical density of the printed image on such multi-layer constructions, coated on a reflective support, is compromised when colorants penetrate into the porous ink-retaining layer.
U.S. Pat. Nos. 4,785,313, 4,832,984, and 6,013,354 disclose recording media comprising a base, an ink-receptive layer that is transparent, and an overcoat layer of fusible fine particles. This type of multi-layer structure has the advantage of being suitable for both transmissive and reflective applications. Both layers are free of light scattering after fusing and, therefore, the image provides higher optical density than the multi-layer construction consisting of a porous ink-retaining layer as described in the previous paragraph. What has been experienced with such media, however, is that the composition of the transparent underlying layer can adversely affect the coating quality of the top fusible layer, the adhesion of the top layer to the substrate, and the image fastness on long-term keeping.
It is an object of this invention to provide a novel porous inkjet recording element that absorbs inks instantly, and after imaging, provides an image which has good quality and is water and abrasion resistant. It is another object of the invention to provide a porous inkjet recording element that is resistant to delamination by customer handling and to image change from long-term keeping.